The present invention relates to power amplification and more particularly to an arrangement to provide high power amplification of a microwave system.
Present day high power amplifiers make use of power combining arrangements. Present day arrangements of power combining and the relative advantages and disadvantages are: (1) parallel, or branching, circuits which employ a number of power splitters or hybrid couplers configured to provide a number of parallel paths emanating from, or converging to, a single port. By employing one branching circuit as a divider and terminating each output with an amplifier and finally recombining the amplified signals with an identical branching circuit, a high power two port amplifier is attained. Advantages include planar realizability, conceptual simplicity, potentially unlimited power addition, and modular. Disadvantages in practice are high loss for large numbers of amplifiers versus size, constructual complexity for high density junction types, interaction effects resulting in high VSWR (voltage standing wave ratio) spikes and/or low isolation spikes, internal dissipation in types using power dividers with ungrounded resistors, unrealizability in series resistor layout for certain planar dividers. (2) Series-fed arrays including a cascade of directional couplers with progressively decreasing coupling coefficients such that equal power results at all output ports (coupled ports). Phase, however, varies in a systematic way from output to output. A two port high power amplifier is attained by terminating each coupled port with identical amplifiers and combining their outputs with an identical type series coupler array reversed end-to-end with respect to the input array. Advantages include potentially unlimited power combining, all internal terminations are grounded, simple design equations for coupling array, easily incremented in power. Disadvantages include power loss due to coupling variations resulting from tolerance and frequency law of coupling, for large numbers of amplifiers the coupling coefficients become very small and difficult to control in construction and variations of coupling characteristics (flatness, VSWR, phase and directivity) with coupling coefficient. (3) Multi-element combining employs an array of amplifier elements around the perimeter or cross-section of a transmission line. Advantages could include compactness, and low loss. Disadvantages include physical limit on the number of elements that can be packaged on a transmission line perimeter, low or undesirable impedance level seen by active elements and higher mode spurious responses.